U.S. patent number 6,896,751 [Application Number 10/439,015] was granted by the patent office on 2005-05-24 for energetics binder of fluoroelastomer or other latex.
This patent grant is currently assigned to Universal Propulsion Company, Inc.. Invention is credited to Mark Clark, Jim Cornwell, Philip L. Posson.
United States Patent |
6,896,751 |
Posson , et al. |
May 24, 2005 |
Energetics binder of fluoroelastomer or other latex
Abstract
A propellant composition including a fuel, an oxidizer, and a
latex binder and method of making, wherein the method of making
eliminates the need for the large amounts of volatile, flammable
solvents that are typically associated with the traditional
process.
Inventors: |
Posson; Philip L. (Cave Creek,
AZ), Clark; Mark (Glendale, AZ), Cornwell; Jim
(Glendale, AZ) |
Assignee: |
Universal Propulsion Company,
Inc. (Phoenix, AZ)
|
Family
ID: |
33417700 |
Appl.
No.: |
10/439,015 |
Filed: |
May 16, 2003 |
Current U.S.
Class: |
149/19.92;
149/109.6 |
Current CPC
Class: |
C06B
21/0025 (20130101) |
Current International
Class: |
C06B
21/00 (20060101); C06B 045/10 (); D03D
023/00 () |
Field of
Search: |
;149/19.92,109.6 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Web Page for Tecnoflon TN Latex Fluoroelaster Specialty Polymer
(http://www.ausimont.com/docs/spec_tnlatex.html), printed Aug. 27,
2002..
|
Primary Examiner: Felton; Aileen
Attorney, Agent or Firm: Holden; Jerry
Claims
What is claimed is:
1. A method of making a propellant composition, comprising the
following steps: mixing a latex binder with a nonsolvent liquid to
provide an extended latex binder; blending the extended latex
binder, a fuel, and an oxidizer to form a slurry; adding a solvent
to the slurry to destabilize the extended latex binder; agitating
the slurry to provide a mixed, thickened slurry; and, optionally,
reducing the solvent content to facilitate further processing by
means of vacuum or ventilation; and drying, extruding, or otherwise
processing the solid material by conventional means, either to make
it suitable for further processing, or by shaping and/or placing it
in a form, cup, or other device which can be used in a pyrotechnic
product or device.
2. The method of claim 1, wherein the step of mixing a latex binder
with a nonsolvent liquid further comprises adding water.
3. The method of claim 1, wherein the nonsolvent liquid comprises
denatured methyl alcohol, ethyl alcohol, butanone, acetonitrile, or
a mixture thereof and wherein the solvent comprises acetone, methyl
ethyl ketone, ethyl acetate, butyl acetate, propyl acetate, methyl
t-butyl ether, methyl t-amyl ether, tetrahydrofuran, supercritical
fluids, or mixtures thereof.
4. The method of claim 1, wherein the latex binder is selected from
the group consisting of fluoroelastomers, latex forms of acrylic
resins, polyvinyl butyral, carboxy modified rubber, nitrile
modified rubber, polyvinyl chloride, polybutadiene,
acrylonitrile-styrene-butadiene, vinyl pyridine, styrene butadiene
polymer latex, and compatible mixtures thereof.
5. The method of claim 1, wherein the step of adding a solvent to
the slurry to destabilize the extended latex binder comprises
adding the solvent in an amount of about 2 times or less the volume
of the slurry.
6. A method of making a propellant composition, comprising the
following steps: providing a latex binder; blending the latex
binder in a non-gelling extender to form an extended latex binder;
mixing the extended latex binder, a fuel, and an oxidizer to form a
slurry; adding a solvent to the slurry; mixing the slurry; and
processing the slurry to provide the propellant composition.
7. The method of claim 6, wherein the latex binder is selected from
the group consisting of fluoroelastomers, latex forms of acrylic
resins, polyvinyl butyral, carboxy modified rubber, nitrile
modified rubber, polyvinyl chloride, polybutadiene,
acrylonitrile-styrene-butadiene, vinyl pyridine, styrene butadiene
polymer latex, and compatible mixtures thereof.
8. The method of claim 6, wherein the step of providing the latex
binder comprises providing the later binder in the form of a fluid,
subdivided solid, dispersion, or solution.
9. The method of claim 6, wherein the non-gelling extender
comprises a low molecular weight aliphatic alcohol.
10. The method of claim 6, wherein the step of blending the latex
binder further comprises providing the non-gelling extender in an
amount of about 5 percent to about 60 percent by weight of the
latex binder.
11. The method of claim 6, further comprising the step of blending
the latex binder in a non-gelling extender further comprises adding
water to form the extended latex binder.
12. The method of claim 11, wherein the water is present in an
amount of about 30 percent to about 60 percent by weight of the
extended latex binder.
13. The method of claim 6, wherein the step of mixing is performed
with sufficient shear to break up agglomerates.
14. The method of claim 6, wherein the step of adding a solvent
comprises adding an amount of solvent about half or less the volume
of the slurry.
15. The method of claim 6, wherein the solvent is selected from the
group consisting of acetone, methyl ethyl ketone, ethyl acetate,
butyl acetate, propyl acetate, methyl t-butyl ether, methyl t-amyl
ether, tetrahydrofuran, supercritical fluids, and mixtures
thereof.
16. The method of claim 4, wherein the latex binder is selected
from the group consisting of fluoroelastomers, latex forms of
acrylic resins, and mixtures thereof.
17. A method of making a propellant composition, comprising the
following steps: providing a latex binder; blending the latex
binder in a non-gelling extender to form an extended latex binder
solution; mixing the extended latex binder solution, a fuel
comprising a metallic powder selected from the group consisting of
silicon, boron, aluminum, magnesium, titanium, and mixtures
thereof, and an oxidizer to form a slurry; adding a solvent to the
slurry in an amount of about a quarter or less of the volume of the
slurry; mixing the slurry; and processing the slurry to provide the
propellant composition.
18. The method of claim 17, wherein the step of blending the latex
binder in a non-gelling extender to form an extended latex binder
solution further comprises adding water in an amount of about 30
percent to 80 percent by weight of the extended latex binder
solution.
19. The method of claim 17, wherein the step of providing a latex
binder comprises providing a terpolymer of hexafluoropropylene,
vinylidene fluoride, and tetrafluoroethylene.
20. The method of claim 19, wherein the terpolymer comprises about
40 to 80 percent solids and about 80 to 40 percent fluorine by
weight of the terpolymer.
21. The method of claim 17, wherein the step of providing a latex
binder comprises the steps of: providing an acrylic polymer;
providing a plasticizer; forming the latex binder by mixing the
acrylic polymer and plasticizer with an emulsifier.
22. The method of claim 17, wherein the latex binder is present in
an amount of about 5 percent to 15 percent by weight of the slurry.
Description
FIELD OF THE INVENTION
The present invention relates to a pyrotechnic composition and the
method for making the composition that includes a fuel, an
oxidizer, and a latex binder. The method of the invention reduces
the need for large amounts of volatile, flammable solvents that are
typically associated with the traditional "shock gelling" process.
In particular, the method of the invention involves mixing a latex
binder and a compatible nonsolvent organic fluid to provide an
extended binder that is mixed with a fuel and an oxidizer to
provide a propellant composition, then treating the mixture with a
gellant liquid to provide a thick, uniform, dough-like material
that is ready for further processing.
BACKGROUND OF THE INVENTION
Propellant compositions have a wide variety of uses, for example,
inflation, expulsion, and flotation devices, such as vehicle
occupant restraint bags, and commercial and military devices, such
as fire suppression devices, piston operated mechanical devices,
rocket engines, and munitions. As a result of the diversity and
desirability of these compositions, manufacturers strive to improve
production methods, reduce costs and waste, and increase
safety.
Pyrotechnic propellant compositions typically include a fuel,
usually metallic in nature, an oxidizer, and optionally, a binder
system that serves as an adhesive, holding the fuel and oxidant in
a well-mixed condition. Without a binder, many compositions
separate under the influence of gravity or vibration, resulting in
performance degradation. In addition, the binder may serve as part
of the fuel, and aid in maintaining the final product in a defined
physical condition. The binder often causes changes in the burning
rate of the composition, so that binder concentrations must be
substantially uniform throughout the mass of composition for
controllable performance. Therefore, proper mixing and
incorporation of the binder during manufacture are key process
parameters.
One known method for manufacturing propellant compositions involves
dissolving a binder in acetone or other solvent and loading the
solution into a muller-type mixer prior to addition of the fuel
particles or oxidizer. The concentration of binder in the fluid is
typically 10-20%, to keep the viscosity of the fluid down in a
convenient working range. Fine metallic powder or other fuel is
then added to the mixer, and after a time, an oxidizer, such as
polytetrafluoroethylene (PTFE) or a metal salt oxidizer, is also
loaded into the mixer. The slurry is mixed until the solvent
evaporates to form a dough-like consistency, which is spread on
trays and placed in large ovens for complete drying. After drying,
the cakes are granulated for feedstock to the process. The process
is time consuming and labor intensive. In addition, process workers
are exposed to high-hazard conditions.
Another process for manufacturing propellant compositions uses a
"shock precipitation" or "Cowles Dissolver" method, as shown in
FIG. 1. U.S. Pat. No. 3,876,477 describes a process wherein the
binder is dissolved in acetone and placed in a Cowles Dissolver.
The fuel and oxidizer components are then suspended in the binder
solution and a countersolvent is added while mixing the solution. A
large amount (about 4 times the volume of the solution) of
countersolvent, e.g., hexane, causes the binder to precipitate from
the solvent. As the binder precipitates, the active particles are
entrapped in the binder. The solids are then filtered, dried, and
pressed or extruded. This process, is also time consuming and
results in major waste disposal problems with the large amounts of
volatile, flammable solvents used during the process. When
performed manually, the operator is also at risk because of the
close proximity to the mixing process and the large volume of
solvent, as well as the propellant particles. U.S. Pat. No.
6,132,536 also discloses a shock precipitation method, however, the
process is automated to reduce safety concerns with the manual
process.
Thus, there remains a need for a less-hazardous, less expensive
method for making a propellant composition with no reduction of
pyrotechnic properties associated with the more hazardous and
costly methods currently used. It would be desirable to accelerate
production, and avoid the use of large quantities of volatile
solvents and the safety hazards associated therewith. The present
invention provides a method for manufacturing propellant
compositions that reduces the amount of volatile solvent used,
accelerates the processing time, and increases process safety.
SUMMARY OF THE INVENTION
The present invention is directed to a pyrotechnic composition and
methods for its manufacture.
One embodiment of the invention relates to a propellant composition
having a latex binder extended with a nonsolvent organic liquid, a
second gellant liquid, an oxidizer, and a fuel. The composition
also may have chemical modifiers such as plasticizers, curing
agents, catalysts or burn rate modifiers, antioxidants, or
dispersants. In addition, the composition also may have processing
aids such as lubricants, anti-static agents, mold release
agents.
Some embodiments of the invention are directed toward particular
types of one or more constituents of the composition. For example,
in one embodiment of the invention the nonsolvent organic liquid
may be denatured methyl alcohol, ethyl alcohol, isopropyl alcohol,
or a mixture of these alcohols. In yet another embodiment, the
latex binder is selected from fluoroelastomers, latex forms of
acrylic resins, polyvinyl butyral, carboxy modified rubber, nitrile
modified rubber, polyvinyl chloride, polybutadiene,
acrylonitrile-styrene-butadiene, vinyl pyridine, styrene butadiene
polymer latex, and compatible mixtures thereof.
In yet another embodiment, the oxidizer is selected from
1,3,5-trinitro-1,3,5-triaza-cyclohexane,
1,3,5,7-tetranitro-1,3,5,7-tetraaza-cyclooctane, ammonium
dinitramide, 1,3,3-trinitroazetidine, potassium nitrate, and
mixtures thereof. Moreover, in one embodiment of the invention the
fuel contains at least one metal such as silicon, boron, aluminum,
magnesium, and titanium, aluminum-magnesium alloy, or titanium
hydride.
Another embodiment of the present invention relates to methods for
making the compositions described above. For example, one method
involves the steps of mixing a latex binder with a nonsolvent
liquid to provide an extended latex binder, blending the extended
latex binder with a fuel and an oxidizer to form a slurry, adding
solvent to the slurry to destablize the extended latex binder and
agitating the slurry to form a mixed, thickened slurry. The
composition is then dried, extruded, shaped, formed, or otherwise
processed for use in a pyrotechnic product or device.
Some embodiments of the invention further define some of the steps
described above or include additional steps. For instance, after
solvent is added to the slurry to destabilize the extended latex
binder and to form a mixed, thickened slurry, the solvent level of
the slurry may be reduced, such as by vacuum or ventilation. In one
embodiment, the amount of solvent added to the slurry to
destabilize the extended latex binder is about 2 times or less the
volume of the slurry. In yet another embodiment the step of mixing
a latex binder with a nonsolvent liquid further comprises adding
water.
As described above for the inventive composition, some embodiments
of the inventive method relate to particular types of one or more
constituents of the composition, such as the types of nonsolvent
organic liquids, latex binders, oxidizers, or fuels that may be
used in making the composition. For instance, in one embodiment the
nonsolvent liquid comprises denatured methyl alcohol, ethyl
alcohol, 2-butanone, acetonitrile or a mixture thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
Further features and advantages of the invention can be ascertained
from the following detailed description that is provided in
connection with the drawings as described below:
FIG. 1 is a flow diagram illustrating a prior art process of making
a propellant composition; and
FIG. 2 is a flow diagram illustrating the process of making a
propellant composition according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is directed to a pyrotechnic composition and
method for making the composition that overcomes or reduces the
environmental and safety issues associated with the current methods
without sacrificing the beneficial properties of the propellant or
pyrotechnic. In one embodiment, the composition of the present
invention is based on an extended binder, emulsion, or dispersion,
a primary fuel, an oxidizer, and a gellant for the binder. Optional
additional additives, such as plasticizers, metal reaction
stabilizers, curatives, antioxidants, burn rate catalysts, and cure
catalysts may also be added to the compositions of the
invention.
The method is particularly applicable to the preparation of metal
powder/oxidant/polymer pyrotechnic blends, but may also be used to
coat any particles in general with a polymeric binder. For example,
the method can be used to coat metallic particles to inhibit air
oxidation during storage, or to prepare metal powder compositions
that are injection moldable.
Binder(s)
A binder component is used in the compositions of the invention to
hold the reactive materials together in the finished propellant
form. In this capacity, the binder allows shaping or forming of the
propellant composition into a substantially nonporous solid mass. A
binder also typically helps supply the necessary physical integrity
required to help survive vibration and other disruptive forces that
may occur. In some cases, oxygen, chlorine, or fluorine in the
binder act as auxiliary oxidizers for the metal fuel.
The binder compound may be selected to minimize water vapor
production on combustion. Binders with a reduced potential for
water vapor formation include fluorocarbons and fluorocarbon
elastomers, chlorinated materials such as poly (vinyl chloride or
vinylidene chloride) copolymers, polyacrylonitrile copolymers, and
polyesters such as poly (hydroxyacetic/lactic acid).
The binder systems of the invention are preferably in the form of a
latex, i.e., an emulsion of the polymer in water, and extended with
a compatible fluid. The binder system used in the composition
includes at least a binder, or binder resin, and various additional
components. Suitable binders, include, but are not limited to,
fluoroelastomers, latex forms of acrylic resins, polyvinyl butyral,
carboxy modified rubber, nitrile modified rubber, polyvinyl
chloride, polybutadiene, acrylonitrile-styrene-butadiene, vinyl
pyridine, styrene butadiene polymer latex, oxidized polyolefins, or
compatible mixtures thereof.
In one embodiment, the binder includes a terpolymer of
hexafluoropropylene, vinylidene fluoride and optionally
tetrafluoroethylene. The binder systems of the present invention
are preferably solvent free, highly concentrated water based
emulsions of a fluoroelastomer terpolymer. The fluoroelastomer
terpolymer may have a solids content of about 40 to about 80 weight
percent and a fluorine content of about 80 to about 40 weight
percent of the polymer. In one embodiment, the solids content is
about 60 to about 75 weight percent and the fluorine content is
about 75 to about 60 weight percent of the polymer. In another
embodiment, the solids content is about 70 percent or greater by
weight of the polymer and the fluorine content is about 68 percent
or greater by weight of the polymer. A commercial example of a
fluoropolymer latex suitable for use with the present invention is
manufactured by Ausimont USA of Thorofare, N.J. under the tradename
Technoflon Tenn.
In one embodiment, the binder may include specially-made emulsions.
For example, a Hi-Temp.TM. acrylic polymer with a suitable
plasticizer as described below, e.g., di octyl adipate (DOA), may
be made into a latex with an emulsifier, e.g., TRITON X-100.RTM.,
for the production of pressable or extrudable pyrotechnic
compositions. In another example, curing-type binder systems, such
as a dimmer acid/epoxidized vegetable oil/metal carboxylate may
also be emulsified.
As mentioned above, binders also act to hold the reactive materials
together and maintain a shaped propellant composition in finished
form to help control combustion. In one embodiment, the binder
system may be mixed and later cured so that the physical shape of
the product is easily maintained. For example, an emulsified
mixture of maleic anhydride-terminated and hydroxy-terminated
polybutadiene plus a fatty tertiary amine catalyst may serve to
retain the shape of the product.
Chemical stability of the binder systems used in the present
invention is also important so that they will not react with the
oxidizer component prior to combustion. The determination of the
appropriate binder type and other binder system components, and
amounts suitable for use therewith, will be readily understood by
one of ordinary skill in the art when selected according to the
teachings herein.
In one embodiment, the binder is present in an amount about 25
percent or less of the total composition. Preferably, the binder is
included in the composition in an amount about 10 percent or less
by weight of the total composition. In another embodiment, the
binder is present in an amount from about 5 percent to 15 percent
by weight of the composition.
Primary Fuel
Any form of an active fuel component is suitable for forming the
pyrotechnic compositions of the invention. In one embodiment, the
active fuel component is in powder form. In another embodiment, the
fuel component is a metallic powder. Oxidizable inorganic fuels,
preferably of metals or metalloids, such as silicon, boron,
aluminum, magnesium, and titanium, may be used as primary fuel
sources. In one embodiment, aluminum powder is used in combination
with the oxidizer.
The concentration of the fuel component may vary depending on the
type or types of fuel components selected. Any concentration of
active fuel components suitable for combustion may be employed;
however, an active fuel component is typically present in a
concentration of greater than about 5 percent, preferably greater
than about 8 percent, and more preferably greater than about 12
percent by weight of the pyrotechnic composition, and/or is
preferably present in a concentration of about 60 percent or less,
more preferably about 40 percent or less, and even more preferably
about 38 percent or less by weight of pyrotechnic composition. In
one embodiment, the composition includes about 5 percent to about
50 percent of the fuel component by weight of the total
composition. In another embodiment, the fuel component is present
in an amount from about 10 percent to about 35 percent by weight of
the total composition.
The size and shape of the active fuel component particles may be
any size and/or shape suitable for combustion. In one embodiment,
the particle size is greater than about 3 .mu.m in diameter. In
another embodiment, the particle size is about 10 .mu.m or greater.
In yet another embodiment, the particle size is about 100 .mu.m or
less, preferably less than about 50 .mu.m or less, and more
preferably less than about 30 .mu.m or less.
Oxidizer
Oxidizing agents assist in the combustion of fuel compounds of the
pyrotechnic composition. Thus, an oxidizing agent may be used in
the pyrotechnic compositions of the invention to accelerate
combustion, thus facilitating more rapid gas and heat
generation.
Suitable oxidizing agents include, but are not limited to, alkali
metal nitrates, bromates, chlorates, perchlorates, or mixtures
thereof. Specific examples of suitable oxidizing agents include,
but are not limited to, potassium nitrate, potassium perchlorate,
sodium nitrate, lithium nitrate or perchlorate, ammonium
perchlorate ammonium nitrate, barium nitrate, strontium nitrate and
(basic) cupric nitrate. The oxidizer(s) used in the propellant
compositions of the present invention may also include solid
nitramines such as 1,3,5-trinitro-1,3,5-triaza-cyclohexane (RDX),
1,3,5,7-tetranitro-1,3,5,7-tetraaza-cyclooctane (HMX), ammonium
dinitramide (ADN), 1,3,3-trinitroazetidine, and mixtures
thereof.
The oxidizer of the present invention may also be an inorganic
halogen-containing component, such as the halides disclosed in
co-pending U.S. patent application Ser. No. 10/197,468, filed Jul.
18, 2002, entitled "High Density-Impulse Propellant With Minimal or
No Toxic Exhaust Products," which is incorporated in its entirety
by reference herein. In this embodiment, the halide-containing
oxidizer is preferably bromate or iodate. In one embodiment, the
inorganic halogen-containing component is an alkaline bromate,
e.g., lithium bromate (LiBrO.sub.3) potassium bromate (KBrO.sub.3),
sodium bromate (NaBrO.sub.3), or cesium bromate (CsBrO.sub.3). In
another embodiment, the inorganic halogen-containing component is
an alkaline earth bromate, e.g., magnesium bromate
(Mg(BrO.sub.3).sub.2), calcium bromate (Ca(BrO.sub.3).sub.2),
strontium bromate (Sr(BrO.sub.3).sub.2), and barium bromate
(Ba(BrO.sub.3).sub.2).
The slower-acting oxidizing agents, such as potassium nitrate
(KNO.sub.3), may also be combined with combustion accelerants or
other alkaline earth halates, e.g., KBrO.sub.3, to increase the
combustion rate. Measurement of the combustion rate and
optimization thereof are readily understood by those of ordinary
skill in the art. In addition, other oxidizers, such as those
listed above, may be blended with the bromate and/or iodate to
reduce the density-impulse while still providing other desirable
performance characteristics.
The oxidizing agent may be present in any amount suitable for
assisting combustion of the active fuel component. In one
embodiment, the oxidizing agent is present in an amount greater
than about 40 percent, preferably greater than about 50 percent,
and even more preferably greater than about 60 percent by weight of
the propellant composition. In another embodiment, the oxidizer is
present in an amount of about 95 percent or less, preferably about
85 percent or less, and even more preferably about 80 percent or
less by weight of the propellant composition. In yet another
embodiment, the oxidizer is present in an amount from about 60 to
about 90 weight percent of the composition, preferably in an amount
from about 70 to about 80 weight percent of the composition. In
still another embodiment, the oxidizer is present in an amount from
about 80 to about 90 weight percent of the composition.
Oxidizing agents may be of a form similar to that described for
active fuel components, namely powders or any other suitable form
for forming a pyrotechnic composition mixture. In one embodiment,
the oxidizing agent is in powder form with particle size of about 3
.mu.m or greater in diameter, preferably about 4 .mu.m or greater,
and even more preferably about 5 .mu.m or greater. In another
embodiment, the particle size of the oxidizer is about 200 .mu.m or
less in diameter, preferably about 80 .mu.m or less, and more
preferably about 50 .mu.m or less.
Additional Components
Various additional components may also be used in the binder system
or propellant composition to improve the physical properties of the
propellant. For example, plasticizers and processing aids may also
be added to the composition to enhance processing. The binder
system may include one or more of a curing or bonding agent, a cure
catalyst, an antioxidant, an opacifier, or a halide scavenger, such
as potassium or lithium carbonate. Generally, curing agents,
plasticizers, or other processing aids are optionally present in
the composition from about 15 weight percent or less, based on the
total weight of the composition.
The additives may be introduced in the diluent when extending the
binder or with the solvent during high-shear mixing. For example, a
binder modifier resin may be used, such as a high molecular weight
fluoroelastomer Dyneon THV 220A manufactured by Dyneon of Decatur,
Ala., or Viton GLT manufactured by the DuPont Company.
Energetic and nonenergetic plasticizers may be added to the binder
system, depending on whether the propellant composition is intended
to be low energy or high energy. Suitable energetic plasticizers
include, but are not limited to, bis(2,2-dinitropropyl)
acetal/bis(2,2-dinitropropyl)formal (BDNPF/BDNPA),
trimethylolethanetrinitrate (TMETN), triethyleneglycoldinitrate
(TEGDN), diethyleneglycoldinitrate (DEGDN), nitroglycerine (NG),
1,2,4-butanetrioltrinitrate (BTTN), alkyl nitratoethylnitramines
(NENA's), or mixtures thereof. Typical nonenergetic plasticizers
include triacetin, acetyltriethylcitrate (ATEC), dioctyladipate
(DOA), isodecyl perlargonate (IDP), dioctylphthalate (DOP),
dioctylmaleate (DOM), dibutylphthalate (DBP), ethylene carbonate,
propylene carbonate, or mixtures thereof. In one embodiment, the
plasticizer is present in an amount about 10 percent or less by
weight of the propellant composition. In another embodiment, the
plasticizer is present in an amount less than 5 percent by weight
of the propellant composition.
Antioxidants, curing agents, and catalysts may be present in a
total amount about 5 percent or less by weight of the total
propellant composition, and, more preferably, about 2 percent or
less by weight.
When a curing agent is used, a cure catalyst is preferably also
included to accelerate the curing reaction between the curable
binder and the curing agent. Suitable cure catalysts may include
alkyl tin dilaurate, metal acetylacetonate, or triphenyl bismuth.
The cure catalyst, when used, is generally present from about 0.01
percent to about 2 percent by weight, and, preferably, from about
0.01 percent to about 1 percent by weight of total propellant
composition. In another preferred embodiment, the cure catalyst is
present in an amount about 0.05 weight percent or less.
Finely divided high energy additives, such as metallic particles,
may be used to increase the combustion rate of the propellant
composition of the present invention. In one embodiment, the
metallic particles or powders are in the micron-scale range.
Metallic nanoparticles are also contemplated by the present
invention. In one embodiment, metallic nanoparticles are used to
produce a burning propellant with a low burn rate/pressure slope.
Since metallic nanoparticles are smaller in diameter than even the
ultrafine metal powders currently available, their surface area per
volume, and reactivity, is immensely greater. A higher burning rate
increases the rapid initiation rate that a propellant can achieve,
as shown with conventional pyrotechnic propellants. When such
nanoparticles are used, a corrosion-preventative additive should be
used, such as an alkali sebacate, silicate, molybdate, compatible
salt of an organic phosphate ester, octylphosphonic acid or an
imidizole compound such as Sarcosyl (Ciba Geigy) or nitromethane as
an absorptive corrosion inhibitor.
A catalyst or modifier may also be used in the composition of the
invention to increase the burn rate of the composition.
Non-limiting examples of suitable burn rate catalyst/modifiers
include iron oxide (Fe.sub.2 O.sub.3), K.sub.2 B.sub.12 H.sub.12,
Bi.sub.2 MoO.sub.6, ferrocene (Fe(C.sub.5 H.sub.5).sub.2),
chromium, copper, graphite, carbon powders, and carbon fibers.
The addition of lubricants in the propellant compositions of the
present invention may help reduce friction as the crystals slip
past one another and, thus, prevent unwanted accidental reaction.
Because of this reaction prevention mechanism, the friction
sensitivity of the propellant composition may be reduced. For
example, the minimum allowable friction sensitivity for shipping is
80 Newtons using the UN friction testing apparatus. The addition of
a lubricant into the propellant composition of the invention may
improve the measured value by about 10 to about 30 percent. Thus, a
composition having a non-allowable or non-measurable friction
sensitivity using the UN friction testing apparatus may be improved
and, thus measurable, with the addition of an internal lubricant.
Suitable solid lubricants are graphite or hexagonal boron nitride,
or castor oil-derived wax.
When used, the addition of lubricants may generally be present in
an amount about 0.1 percent or greater. In one embodiment, the
lubricant(s) is present in an amount about 10 percent or less.
Antioxidants may also be used in the binder system. Suitable
antioxidants may include 2,2'-bis(4-methyl-6-tert-butylphenol)
available from American Cyanamid Co. of Parsippany, N.J. under the
tradename AO-2246, 4,4'-bis(4-methyl-6-tert-butylphenol), BHT, BHA,
or mixtures thereof. In one embodiment, the antioxidant is present
in an amount of about 0.05 percent to about 1 percent by weight of
the total propellant composition. In another embodiment, the
antioxidant is present in an amount about 0.5 percent or less by
weight of the total propellant composition.
An opacifier, e.g., carbon black, also may be used in the binder
system, generally in an amount from about 0.01 percent to 2 percent
by weight. Preferably, the opacifier is present in an amount about
1 percent by weight or less.
Dispersants may also be added to a powder/solvent mixture to reduce
agglomeration tendency of individual particles during processing.
For example, a dispersant tends to disperse and subdivide
individual active fuel/additive/oxidizer agglomerates and thus to
increase the degree of incorporation with other components. The
agents also have utility as a coupling agents, increasing the
practical utility of the bond between polymeric binder and active
fuel and or oxidizer particles. A dispersing agent also tends to
reduce the apparent viscosity of a powder/solvent mixture, and
consequently the already-small amount of solvent required to
process the mixtures of the invention.
Non-limiting examples of dispersing agents include organotitanates,
lecithin, complete or partial fatty acid esters of polyhydroxy
compounds, soluble fluorocarbon materials containing integral polar
molecular entities, the alkylamine adducts of dimer acid, alkylated
polyvinyl pyrrolidines, cationic surfactants such as lauryl
pyridinium chloride, ethoxylated soya amine, TRITON X-400
quaternary chloride available from Rohm and Haas of Philadelphia,
Pa., certain copolymers of ethylene and propylene oxide, alkyl
polyoxyalkylene phosphates, and SURFYNOL 104 tertiary acetylenic
glycol available from Air Products of Allentown, Pa. Although any
suitable concentration may be used, dispersant agents are
preferably present in an amount from about 0.01 percent to about 3
percent, preferably about 0.05 percent to about 1.5 percent, and
more preferably about 0.1 percent to about 1 percent by weight of
the composition.
Fine reinforcing fibers may also be dispersed in the pyrotechnic
composition in a proportion that advantageously enhances the
physical and safety aspects of the finished product. In this aspect
of the invention, the oxidizer content may be slightly increased to
ensure complete combustion or destruction of the added fibers. The
fibers are preferably use in the composition in an amount of about
0.1 percent to about 3 percent, though amounts less than about 0.1
percent and greater than about 3 percent, by weight of the
compositions are also contemplated by the present invention.
Suitable fibers include, but are not limited to, high-tenacity
polyester, cellulose or cellulosic derivative, polyamide,
polyolefin, polyacrylonitrile, Rayon, acrylic copolymers, and
mixtures thereof.
In addition, any suitable mold release agent known in the art may
be added to the compositions of the invention. For example, mold
release agents such as ethylene bisstearamide manufactured by Lonza
Group of Switzerland under the trade name Aacrawax C Atomized,
polytetrafluroethylene ("PTFE") powders, zinc stearate, calcium
stearate, low molecular weight polyolefin powder, low molecular
weight polyolefin dispersions, pentaerythritol tetrastearate, and
mixtures thereof may be used. Mold release agents may be employed
in any suitable concentration. In one embodiment, the mold release
agent is present in an amount of about 0.05 percent to about 2
percent, preferably about 0.1 percent to about 1 percent, and more
preferably about 0.2 percent to about 0.6 percent by weight of the
propellant composition.
Production Method
The pyrotechnic composition of the invention may be made according
to the following steps: (1) providing a latex binder and blending
it in a suitable non-gelling extender; (2) blending the extended
latex binder, a fuel, an oxidizer and optional modifying
ingredients to form a slurry; (3) adding a small amount of solvent
to the slurry to destabilize the extended latex binder and mixing
the ingredients by agitation or other suitable means to provide a
thickened slurry; and (4) drying, granulating, pressing and/or
extruding the product. The thickened slurry may also be extruded as
such into a housing such as a booster cup, or to act as a
stand-alone energetic unit upon final evaporation of the solvents
present.
In Step 1, the binder of the present invention may be applied to or
admixed with the reactive materials of the propellant composition
in any suitable manner, such as including as a fluid, subdivided
solid, dispersion, or solution. In one embodiment, the latex binder
is extended with a nonsolvent liquid. The nonsolvent liquid is a
low molecular weight aliphatic alcohol, e.g., methyl alcohol or
ethyl alcohol or a mixture thereof. The amount of nonsolvent
liquid, preferably about 2 percent to about 70 percent, may also
serve in the extended latex binder mixture to minimize undesired
solubility of the fuel and oxidizer particles. In one embodiment,
the amount of nonsolvent liquid present is about 5 percent to about
60 percent by weight of the solution.
In addition, a small amount of water may be added to the binder.
For example, about 30 percent to about 80 percent by weight of the
extended latex binder may be water. In one embodiment, about 30
percent to about 60 percent by weight of the extended latex binder
may be water.
Step 2 involves blending the latex binder, a fuel, and an oxidizer
to form a slurry. This step is performed with sufficient shear to
break up agglomerates and thoroughly mix the ingredients.
Non-limiting examples of apparatus that may be used to perform this
high shear mixing step include a Simpson Mix-Muller available from
Simpson Group of Aurora, Ill., a Stomacher.RTM. kneading device, a
high shear rotary mixer, or a Hobart.RTM. mixer. When using a high
shear rotary mixer, enough fluid must be present to maintain the
proper viscosity conditions required by the device.
Conventional methods of making pyrotechnic compositions employ
large amounts of solvent, e.g., about 4 times the volume of the
slurry, to help ensure that a binder is distributed over the
surfaces of the active fuel and oxidizer components. The role of
the solvent in the present invention, however, is to destabilize
the extended latex binder and swell the polymer present. Thus, the
amount of solvent is greatly reduced over that of conventional
methods.
Step 3 of the method of the present invention involves adding
solvent to the slurry and agitating, preferably at high shear,
wherein the volume of the solvent is about 2 times or less the
volume of the slurry. In another embodiment, the solvent volume is
about equal to the slurry volume. In yet another embodiment, the
volume of the solvent is about half or less the volume of the
slurry. In still another embodiment, the solvent volume is about a
quarter or less of the slurry volume.
Thus, in one embodiment, the amount of solvent used is about 50
percent or less of the amount of solvent used in conventional
methods. In another embodiment, the solvent used is reduced by
about 70 percent or greater over traditional methods. In yet
another embodiment, the reduction in solvent is about 90 percent or
greater as compared to the amount of solvent used in conventional
methods.
Any solvent suitable for destabilizing the extended latex binder
may be employed in the method of the present invention. It is
preferred that the solvent does not dissolve and/or react with the
fuel(s) and oxidizing agents. This feature aids in maintaining a
small and uniform fuel particle size and, therefore, uniformity of
the fuel composition burn rate.
Suitable solvents include, but are not limited to, acetone, methyl
ethyl ketone, ethyl acetate, butyl acetate, propyl acetate, methyl
t-butyl ether, methyl t-amyl ether, tetrahydrofuran, supercritical
fluids, and/or mixtures thereof. In one embodiment, the solvent
includes acetone.
A solvent or emulsion-breaking agent is typically chosen so as not
to adversely affect the proportion, particle size or chemical
purity of the active fuel or oxidizer. A nonsolvent is also
typically selected so that it does not remove or destroy auxiliary
ingredients such as antioxidants, dispersants, etc. that are
desired to be in the finished composition.
After addition of the solvent, the slurry thickens and mixing
continues with evaporation until a suitable dough viscosity is
obtained for subsequent processing.
Mixing may be performed under vacuum or ventilation, i.e., warm dry
air flow or warm inert gas flow, to evaporate the solvent. As
mentioned above, however, because a reduced amount of solvent is
used, the conventional solvent decanting step is unneeded in the
method of the present invention.
Step 4 involves granulating and drying, pressing, or extruding the
product for use by conventional means. Shaped propellant
compositions may be formed by any suitable shaping method known in
the art including, but not limited to, pressing, molding, casting,
or extrusion techniques. In one embodiment, the propellant
composition is formed by pressing, casting or otherwise producing a
preform of composition that remains substantially damp with process
fluid, removing the process fluid by any suitable method as above,
and then compacting or extruding such preform.
In another embodiment, the propellant composition is extruded by
adding small amounts of the composition, e.g., drops or small
slugs, to a solvent bath. The solvent bath may include any suitable
solvent, such as those discussed above. For example, in one
embodiment, the solvent bath includes acetone. In another
embodiment, the solvent bath includes methyl ethyl ketone (MEK).
The exterior of the particles gel to preserve their shape. In the
event that the shaped particles are removed prior to dissolution,
the granules may be dried thereby forming particles that may be
used as a gas-generating propellant or ignition charge. During the
drying step, a free-flow agent, e.g., graphite or Aluminum Oxide
"C" (Degussa Corporation) may be used to facilitate flow and
increase resistance to static discharge.
EXAMPLES
Embodiments of the present invention may be more fully understood
by reference to the following examples. Table 1 lists the
compositional make-up and amount of mixing solvent typically
employed in conventional processes verses the present invention.
While these examples are meant to be illustrative of propellant
compositions made according to the present invention, the present
invention is not meant to be limited by the following examples. All
parts are by weight unless otherwise specified.
TABLE 1 Propellant Compositions U.S. Pat. U.S. Pat. Present
Component No. 3,876,477 No. 3,725,516 Invention Latex Binder Not
applicable Not applicable 5%-15% Binder 25% Teflon 18.5% Viton 0%
15% Viton A Fuel 20% 18.15% 32% TiH.sub.2 Aluminum Aluminum
Oxidizer 35% 54.6% 63% KCLO.sub.4 Potassium Ammonium Perchlorate
Perchlorate Chemical Modifiers 5.0% 9.1% <25% Mixing Solutions
(Percent Weight of Additive Compounds) Hexane 400% 300% Not
applicable Binder Extender Not applicable Not applicable 15%
ethanol Gellant Not applicable Not applicable 10% acetone
The present invention is further illustrated by the following
Examples:
Example 1
Because fuels such as TiH.sub.2 are dangerous to handle, instead of
fuel an inert black iron oxide powder was used to simulate the fuel
in the present invention. Ethanol was added to Technoflon.RTM.
latex until 23% solids by weight was reached. No gellant was used.
The extended Technoflon.RTM. was mixed with the black iron oxide.
At 8.3% Technoflon.RTM. solids binder, granules were weak and
incompetent.
Example 2
Black iron oxide powder was mixed with ethanol-extended
Fluoroelastomer latex, and granulated at 5.7% binder. The granules
were very lightly agglomerated, soft and fell to powder on
handling.
Example 3
Black iron oxide powder was replaced with a fuel simulant of 60%
zinc powder and 40% atomized aluminum. 0.71 grams of Technoflon TN
fluorocarbon latex and 1.8 grams ethanol were added to 9.5 grams of
the simulant. The composition was mixed and 1.0 grams acetone was
added. The mixture suddenly thickened. Upon drying, the composition
made strong abrasion-resistant granules at 5.0% binder. The
addition of the gellant resulted in large improvements over the
results of Examples 1 and 2.
Example 4
950 grams Zn--Al powder fuel simulant, 71 grams TN latex, 180 grams
ethanol were mixed thoroughly. 100 grams of acetone were then added
to the mixture. The mixture promptly gelled. The mixture was then
dried at 150-Fahrenheit for about 30 minutes. The resulting product
was visually uniform and resisted casual abrasion. The product
formed competent granules, rendered free flowing by addition of
0.1% Aluminum Oxide C. The granules fed well though a vibratory
feeder. In comparison to the prior art "shock gel" process, the
present invention uses 93.4% less solvent.
All patents and patent applications cited in the foregoing text are
expressly incorporated herein by reference in their entirety.
The invention described and claimed herein is not to be limited in
scope by the specific embodiments herein disclosed, since these
embodiments are intended as illustrations of several aspects of the
invention. Any equivalent embodiments are intended to be within the
scope of this invention. Indeed, various modifications of the
invention in addition to those shown and described herein will
become apparent to those skilled in the art from the foregoing
description. Such modifications are also intended to fall within
the scope of the appended claims.
* * * * *
References